The present invention relates to a method for recording a large amount of information on a magnetic recording medium at one time, and in particular, to a method for transferring a recording information to a magnetic recording medium of large capacity and high recording density.
With rapid development and progress in the utilization of digital image, amount of information to be handled in personal computers and other devices has extensively increased. Because of the increase of the amount of information, there are now strong demands on a magnetic recording medium, which has larger capacity to record the information and can be manufactured at low cost and requires shorter time for writing and reading operations.
In a high density recording medium such as hard disk or in a high density floppy disk type magnetic recording medium represented by ZIP (Iomega Inc.), information recording area has narrower track compared with the floppy disk now commonly used. In order that magnetic head can scan over narrow track width and signals can be recorded or reproduced with high S/N ratio, it is necessary to perform accurate scanning by the tracking servo technique.
In a large capacity magnetic recording medium such as a hard disk or a removable type magnetic recording medium, servo signal for tracking or address information signal, reproduction clock signal, etc. are recorded with a certain spacing between them within one turn of the disk. This is the so-called pre-format.
By reading this pre-formatted signal and by correcting its own position, the magnetic head can run accurately on the track.
In the mode of pre-formatting currently in practice, disks are recorded one by one and track by track using a special-purpose servo recorder. However, there are problems in that the servo recorder are expensive and long time is required for the preparation of the pre-format and this means longer time for manufacture and higher manufacturing cost.
In this respect, a method has been proposed to perform magnetic transfer without carrying out pre-format for each track. For example, a transfer technique is described in Japanese Patent Publications Laid-Open 63-183623, 10-40544, and 10-269566. However, none of these inventions provides a proposal suitable for practical applications. There has been no disclosure on concrete means or conditions such as the condition of magnetic field to be applied at the magnetic transfer in the method for magnetic transfer or the means for generating the magnetic field.
To solve the problems as described above, the following method has been proposed in Japanese Patent Publications Laid-Open 63-183623 and 10-40544: On the surface of the substrate, surface irregularities (i.e. recesses and projections; concave portions and convex portions) corresponding to information signals are formed. The surface of the master carrier for magnetic transfer where ferromagnetic thin film is formed at least on the projections is brought into contact with the surface of sheet-type or disk-type magnetic recording medium where ferromagnetic thin film or ferromagnetic powder coating layer is formed. Or, AC bias magnetic field or DC magnetic field is applied to excite ferromagnetic material which constitutes the surface of the projections. As a result, magnetized pattern to match the surface irregularities is recorded on the magnetic recording medium.
According to this method, the surface of the projected portions of the master carrier for magnetic transfer is brought closely together to the magnetic recording medium to be pre-formatted, i.e. the slave medium, and the ferromagnetic material which constitutes the projected portions is excited. As a result, the desired format is formed on the slave medium. By this method, recording can be carried out statically without changing relative positions of the master carrier for magnetic transfer and the slave medium, and accurate pre-format recording can be performed. Also, the time required for the recording is very short. Specifically, in the method for recording from the magnetic head as described above, the time of several minutes to several tens of minutes is normally required, while magnetic transfer can be completed within one second regardless of the recording capacity or recording density in this magnetic transfer method.
Now, description will be given on the transfer of pattern for pre-format in the master carrier for magnetic transfer referring to FIG. 1. FIG. 1(A) is a schematical plan view to explain magnetic layer surface of the master carrier for magnetic transfer, and FIG. 1(B) is a cross-sectional view to explain the process of transfer.
On a certain area of the track of the master carrier 1 for magnetic transfer, a pre-format region 2 and a data region 3 where patterns of servo signals and address signal for tracking to be transferred are formed. By bringing the master carrier 1 for magnetic transfer and the slave medium 4 closely together and by applying an external magnetic field 6 for transfer in track direction 5, the pre-format information can be transferred to the slave medium as a recording information 7. Thus, the slave medium can be manufactured with high efficiency.
However, it has been made clear that, when magnetic transfer is performed according to this method, the quality of information signal may be deteriorated, and that servo action may be inaccurate.
It is an object of the present invention to provide a method and an apparatus for stable magnetic transfer by bringing a master carrier for magnetic transfer and a slave medium closely together and by transferring a pre-format pattern through application of an external magnetic field in order to prevent inaccurate servo operation of the slave medium.
The present invention provides a method for magnetic transfer by bringing a master carrier for magnetic transfer with a slave medium and by applying magnetic field for transfer, said master carrier having a magnetic layer on surface of a substrate corresponding to an information signal, and said slave medium comprising a magnetic recording medium where the information is to be transferred, said method comprising the steps of:
arranging permanent magnets each having magnetic field symmetrical to the axis of the magnetic pole at least on one of upper or lower surfaces of the slave medium with the axis of the magnetic pole disposed in parallel to the surface of the slave medium;
rotating the slave medium or the permanent magnet in track direction;
performing initial DC magnetization on the slave medium in advance in track direction, and bringing the master carrier for magnetic transfer closely together with the slave medium processed by said initial DC magnetization; and
performing magnetic transfer by applying magnetic field for transfer in track direction reverse to the direction of the initial DC magnetization on the surface of the slave medium.
Further, the present invention provides a method for magnetic transfer by bringing a master carrier for magnetic transfer with a slave medium and by applying magnetic field for transfer, said master carrier having a magnetic layer on surface of a substrate corresponding to an information signal, and said slave medium comprising a magnetic recording medium where the information is to be transferred, said method comprising the steps of:
applying magnetic field on the surface of the slave medium in track direction,
performing initial DC magnetization in advance in track direction on the slave medium, and bringing the master carrier for magnetic transfer with the slave medium processed by said initial DC magnetization closely together;
arranging permanent magnets having magnetic field symmetrical to the axis of the magnetic pole at least on one of upper or lower surfaces of the slave medium with the axis of the magnetic pole running in parallel to the surface of the slave medium;
rotating the permanent magnet or the slave medium closely combined with the master carrier for magnetic transfer in track direction; and
performing magnetic transfer by applying magnetic field for transfer in track direction reverse to the direction of the initial DC magnetization.
Also, the present invention provides a method for magnetic transfer as described above, wherein, when said permanent magnets each having magnetic field symmetrical to the axis of the magnetic pole are arranged at least on one of upper or lower surfaces of the slave medium with the axis of the magnetic pole running in parallel to the surface of the slave medium, the magnetic field intensity distribution in track direction of the magnetic field generated is such that there is at least one point where the magnetic field intensity is higher than the coercive force Hcs of the slave medium on a position in track direction.
Further, the present invention provides a method for magnetic transfer as described above, wherein, when said permanent magnets each having magnetic field symmetrical to the axis of the magnetic pole are arranged at least on one of upper or lower surfaces of the slave medium with the axis of the magnetic pole running in parallel to the surface of the slave medium, the magnetic field intensity distribution in track direction of the magnetic field generated is such that magnetic field intensity higher than the coercive force Hcs of the slave medium is present only in one direction on a position in track direction, and the magnetic field intensity in reverse direction is lower than the coercive force Hcs of the slave medium at any position in any track direction.
Also, the present invention provides a method for magnetic transfer as described above, wherein, when said permanent magnets each having magnetic field symmetrical to the axis of the magnetic pole are arranged at least on one of upper or lower surfaces of the slave medium with the axis of the magnetic pole running in parallel to the surface of the slave medium, the magnetic field intensity distribution in track direction of the magnetic field generated is such that magnetic field intensity higher than the maximum value of the optimal transfer magnetic field intensity range is not present at any position in any track direction, magnetic field intensity within the optimal transfer magnetic field intensity range is present at least at one point in one track direction, and magnetic field intensity in track direction reverse thereto is lower than the minimum value of the optimal transfer magnetic field intensity range at any position in any track direction.
Further, the present invention provides a method for magnetic transfer as described above, wherein the optimal transfer magnetic field intensity is 0.6xc3x97Hcs to 1.3xc3x97Hcs with respect to the coercive force Hcs of the slave medium.
Also, the present invention provides an apparatus for magnetic transfer by bringing a master carrier for magnetic transfer and a slave medium closely together and by applying magnetic field for transfer, said master carrier having a magnetic layer on surface of a substrate corresponding an information signal, and said slave medium comprising a magnetic recording medium where the information is to be transferred, said apparatus comprising initial DC magnetizing means for arranging permanent magnets each having magnetic field symmetrical to the axis of the magnetic pole at least on one of upper or lower surfaces of the slave medium with the axis of the magnetic pole running in parallel to the surface of the slave medium, for rotating the slave medium or the permanent magnet in track direction, and for applying magnetic field in track direction on the surface of the slave medium to perform initial DC magnetization of the slave medium in advance in track direction, combining means for combining the master carrier for magnetic transfer with the slave medium processed by said initial DC magnetization, and transfer magnetic field applying means for applying magnetic field for transfer in track direction reverse to the direction of the initial DC magnetization on the surface of the slave medium.
Further, the present invention provides an apparatus for magnetic transfer by bringing a master carrier for magnetic transfer and a slave medium closely together and by applying magnetic field for transfer, said master carrier having a magnetic layer on surface of a substrate corresponding an information signal, and said slave medium comprising a magnetic recording medium where the information is to be transferred, said apparatus comprising initial DC magnetizing means for applying magnetic field in track direction on the surface of the slave medium and for performing initial DC magnetization in advance in track direction of the slave medium, combining means for combining the master carrier for magnetic transfer with the slave medium processed by said initial DC magnetization, and transfer magnetic field applying means for arranging permanent magnets each having magnetic field symmetrical to the axis of the magnetic pole at least on one of upper or lower surfaces of the slave medium with the axis of the magnetic pole running in parallel to the surface of the slave medium, for rotating said permanent magnets or the collective unit comprising said master carrier for magnetic transfer combined with said slave medium in track direction, and for applying magnetic field for transfer in track direction reverse to the direction of the initial DC magnetization.
Also, the present invention provides an apparatus for magnetic transfer as described above, wherein, when said permanent magnets each having magnetic field symmetrical to the axis of the magnetic pole are arranged at least on one of upper or lower surfaces of the slave medium with the axis of the magnetic pole running in parallel to the surface of the slave medium, magnetic field intensity distribution in track direction of the magnetic field generated is such that magnetic field intensity higher than the coercive force Hcs of the slave medium is present at least at one point on a position in track direction.
Further, the present invention provides an apparatus for magnetic transfer as described above, wherein, when said permanent magnets each having magnetic field symmetrical to the axis of the magnetic pole are arranged at least on one of upper or lower surfaces of the slave medium with the axis of the magnetic pole running in parallel to the surface of the slave medium, magnetic field intensity distribution in track direction of the magnetic field generated is such that magnetic field intensity higher than the coercive force Hcs of the slave medium is present only in one direction at a position in track direction, and magnetic field intensity in reverse direction is lower than the coercive force Hcs of the slave medium at any position in track direction.
Also, the present invention provides an apparatus for magnetic transfer as described above, wherein, when said permanent magnets each having magnetic field symmetrical to the axis of the magnetic pole are arranged at least on one of upper or lower surfaces of the slave medium with the axis of the magnetic pole running in parallel to the surface of the slave medium, magnetic field intensity distribution in track direction of the magnetic field generated is such that magnetic field intensity higher than the maximum value of the optimal transfer magnetic field intensity range is not present at any position in any track direction, magnetic field intensity within the optimal transfer magnetic field intensity range is present at least at one point in one track direction, and magnetic field intensity in track direction reverse thereto is lower than the minimum value of the optimal transfer magnetic field intensity range at any position in any track direction.
Further, the present invention provides an apparatus for magnetic transfer as described above, wherein the optimal transfer magnetic field intensity is 0.6xc3x97Hcs to 1.3xc3x97Hcs with respect to the coercive force Hcs of the slave medium.